Epidemiology and surveillance of West Nile virus in the Mediterranean Basin during 2010-2023: A systematic review

Climate change can cause spatio-temporal shifts in the epidemiology of various vector borne pathogens, especially in vulnerable areas such as the Mediterranean Basin (MB). Among these pathogens, the West Nile virus (WNV) became endemic in the region. This systematic review and meta-analysis study summarizes WNV epidemiology, molecular characteristics, and surveillance in various MB countries, relying on data and scientific articles on WNV published during 2010-2023. The number of published articles varied across the three MB subregions: Southern Europe (n = 153), North Africa (n = 33), and Western Asia (n = 14). During this period, 5765 WNV cases in humans were documented across 19 MB countries with peaks during 2018-2022, mostly in Italy and Greece. The latter had neurological disease in 70.3% of 1868 cases, and a high case fatality rate (13.7%). Fewer WNV cases were reported in North Africa despite having the highest pooled human seroprevalence (15.4%), suggesting potential underdiagnosis and cryptic transmission. Overall, 6.5% out of 160,775 individuals had WNV-IgG antibodies in their sera, and WNV-neutralizing antibodies (NA) were detected in ∼50% of 731 IgG-seropositive individuals, indicating co-circulation of other flaviviruses in the MB. In horses, 698 confirmed cases were reported across 14 MB countries. Compared to humans, horses had a higher pooled IgG (26.0%) and NA (71.8%) prevalence, but a lower case fatality rate (6.1%). Wild birds, the key amplifying hosts, displayed a pooled IgG seroprevalence of 11.9%. WNV-RNA was detected in 4.5% of 3040 dead or neurologically diseased wild birds. Entomological surveillance revealed WNV-RNA in 2.5% of 52,159 mosquito pools tested, mostly Culex pipiens. WNV lineages 1 and 2 co-circulate, with Lineage 2 being dominant in Southern Europe. Surveillance capabilities vary across subregions, with robust integrated strategies in Southern Europe and limited efforts in North Africa and Western Asia. Since no vaccines are available for humans, integrated One Health approaches are crucial for effective surveillance and early warning.